1. Field of the Invention
The present invention relates to a super-regenerative receiver including a super-regenerative oscillator, and more particularly, a super-regenerative receiver which precisely regulates an oscillation condition of a super-regenerative oscillator to improve reception sensitivity and frequency selectivity characteristics.
2. Description of the Related Art
In general, a super-regenerative receiver can be realized with lower costs and fewer components and operated with lower voltage compared to a homodyne or super-heterodyne receiver, and thus is suitable for a communication system that requires a low-cost and low-power receiver. Such a super-regenerative receiver includes a super-regenerative oscillator.
The super-regenerative oscillator is an essential component for realizing the super-regenerative receiver and has advantages such as being operable at a very low bias current (for example, hundreds of μÅ) with a relatively simple structure.
In the meantime, the super-regenerative oscillator has disadvantages such as reverse isolation, sub-harmonic reaction, low reception sensitivity and frequency selectivity. The reverse isolation and sub-harmonic reaction can be overcome using an isolation preamp or an appropriate filter. However, the reception sensitivity or frequency selectivity are characteristic indices sensitive to the form and level of bias current or quench signal. Therefore, in order to improve such characteristics, not only the bias current but also the quench signal of the super-regenerative oscillator needs to be fine-tuned.
FIG. 1 is a block diagram illustrating a conventional super-regenerative receiver.
As shown in FIG. 1, the conventional super-regenerative receiver 100 includes an isolated preamplifier 110, a super-regenerative oscillator 120, an envelope detector 130, a quench generator 140 and a bias current controller 150. The isolated preamplifier 110 amplifies a signal detected from an antenna (not shown) into predetermined gains and at the same time, prevents a signal generated from the super-regenerative oscillator 120 from being delivered back to the antenna. The super-regenerative oscillator 120 receives the amplified signal from the amplifier 110 and generates an oscillation signal according to driving voltage inputted from the quench generator 140 and the bias current controller 150. The envelope detector 130 detects the oscillation signal generated from the super-regenerative oscillator 112 and generates a signal for processing a base band. The operation of the super-regenerative oscillator 120 in the conventional super-regenerative receiver 100 will be explained hereunder in more details with reference to FIG. 2.
FIG. 2 is a detailed block diagram illustrating the super-regenerative oscillator included in the receiver shown in FIG. 1.
Referring to FIG. 2, in the conventional super-regenerative receiver, the super-regenerative oscillator 120 includes an inductor-capacitor (LC) resonance part 121a, an oscillating part 121 and a current mirror part 122. The oscillating part includes a -gm part 121b (-gm meaning transconductance) which generates an oscillation signal using the LC resonance generated in the LC resonance part 121a. The current mirror part 122 provides driving current for oscillation to the -gm part 121b of the oscillating part 121.
The bias current controller 150 receives a signal from the envelope detector 130 (FIG. 1) by feedback to adjust bias current, thereby satisfying the condition for oscillation of the super-regenerative oscillator 120. The super-regenerative oscillator 120 has a predetermined critical level of oscillation, and when the current exceeding the critical level of oscillation is provided to the oscillating part 121, it generates an oscillation signal. In general, the current provided to the oscillating part 121 by the bias current Ib of the bias current controller 150 is determined at somewhat smaller value than the critical level of oscillation. Then, a quench signal Iq is added to the bias current and the resultant sum is provided as the driving current. The driving current is compared with the critical level of oscillation to determine the range of the driving current exceeding the critical level of oscillation. That is, when the quench signal Iq is added to the bias current Ib and the driving current exceeding the critical level is provided to the oscillating part 121 and thereby satisfies the oscillation condition of the oscillating part 121, oscillation begins after a some period of oscillation delay time. When the driving voltage falls back to the level below the critical level of oscillation, the oscillation is terminated. The oscillation delay time and oscillation continuation time are determined according to the range of the driving current exceeding the critical level of oscillation provided to the oscillating part 121. If the desired frequency signal is received, the oscillation delay time is shorter, and the oscillation continuation time is longer. The greater the difference between the received signal and the desired frequency, the longer the oscillation delay time is and the shorter the oscillation continuation time. Here, the envelope detector 130 (FIG. 1) determines whether the desired signal is received or not by integrating the voltage corresponding to the oscillation continuation section by the oscillation continuation time. The oscillation continuation time can be adjusted by manipulating the level of bias current. However, if the bias current is too high, the receiver reacts even to undesired signals. If the bias current is too low, the receiver may not react even to the desired signal. Therefore, the bias current needs to be adjusted to delicately regulate the range of the driving current exceeding the critical level of oscillation.
Conventionally, a current mirror part 122 is used in determining the level of driving current supplied to the oscillating part 121. The current mirror part 122 is composed of two transistors M1 and M2, and according to the ratio of the widths of the two transistors (WM1:WM2=1:N in FIG. 2), the level of driving current provided to the oscillating part 121 is determined. That is, the bias current Ib, supplied by the bias current regulator 150, is multiplied by N times by the current mirror part 122 and provided to the oscillating part 121, thereby determining the range exceeding the critical level of oscillation. Similarly, the quench signal Ib from the quench generator 140 is provided to the oscillating part 121 after multiplied by N times by the current mirror part 122, thereby determining the range exceeding the critical level of oscillation.
As described above, in such a conventional super-regenerative oscillator 120, the bias current Ib from the bias current regulator 150 and the quench signal Iq from the quench generator 140 are simultaneously provided to the current mirror part 122. Thus, the quench signal multiplied by N times N·Iq by the current mirror part 122 is provided to the oscillating part 121. As a result, the oscillation condition of the oscillating part 121 cannot be minutely regulated by adjusting the quench signal Iq, which may cause degradation in the reception sensitivity and frequency selectivity of the receiver.